Fluid operated torque impulse units are known in the art. Examples of such units are shown in U.S. Pat. No. 4,347,902, issued Sept. 7, 1982 to William K. Wallace. Other examples are shown in U.S. Pat. No. 3,116,717 to Donald D. Skoog, U.S. Pat. No. 3,263,449 to Leo Kramer, and U.S. Pat. No. 4,553,948 to Koji Tatsuno.
While previous impulse unit designs have proven generally satisfactory, prior art units do suffer certain disadvantages. Prior designs inherently have a non-symmetrical force distribution between the driving element and the driven element. This creates significant vibration in the units, high internal bearing journal loads and excessive mechanical wear between moving parts.
In the art, there are often requirements for a unit which delivers two torque impulses for each revolution of the driving element, while other requirements employ a single impulse per revolution of the driving element. This has generally required two different fundamental designs of operation, with resulting duplication of cost and effort.
Further, many prior art designs are complicated and expensive to produce. Often, the prior art designs require careful assembly of fragile or awkwardly shaped parts, resulting in costly manufacture. Therefore, a need exists for an impulse unit which overcomes the disadvantages of the prior art.